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ChristianKl comments on 2012 Survey Results - Less Wrong
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Another R issue. How do I convert the scores from IQTest into real numbers? as.numeric seems to do strange things.
use "as.numeric(as.character(dat$IQTest))"
The IQtest data is stored as factor. A factor variable has a set of levels, numbered 1,2,3,... that are the variable can possibly take on and labels for those factors. as.numeric(X) returns the level numbers of X. as.character returns the labels of X. In the case that the labels are actually numbers (usually integers that R is interpreting as character labels for some reason), as.numeric(as.character(X)) will return the numeric values that R is interpreting as labels.
EDIT:
In this case, when no value for IQtest was reported, it was stored as " " instead of "", which made R think the variable contained character data which R defaults to treating as factors. The " "'s should all be NA's once it's converted properly.
"iqt <- as.numeric(dat$IQTest)" The already numeric IQ is in dat$IQ, iqt is only the suspect, online IQtest.
A serious design flaw in S/R means that your code fails badly and silently. The man page suggests that you try as.numeric(factor(5:10)).
Matt Simpson's code is correct. The man page suggests slightly faster as.numeric(levels(dat$IQTest))[dat$IQTest]. That example also shows why they chose the the coercion that they did.